Phosphate treatment is generally used as surface preparation treatment for painting of metal materials. Known examples of such phosphate treatment include zinc phosphate treatment and iron phosphate treatment. After this phosphate treatment, treatment using a chromate solution (chromate treatment) is performed in some cases for the purpose of enhancing corrosion resistance and paint adhesion. However, the chromate solution contains chromium and is therefore environmentally disadvantageous.
From this viewpoint, alternative techniques related to surface treatment agents that could replace the chromate solution have been studied. For example, Patent Literature 1 discloses a composition that contains a fluorine-containing compound, a water soluble and/or water dispersible resin compound having cationic or nonionic properties, phosphoric acid and/or a phosphate compound, and water, and that has an adjusted pH of 1 to 6 (see claim 1).